The invention relates to a method for printing on a substrate.
The control of print-related processes, such as for example a color register control or a color density control, usually takes place using print control marks printed on a substrate, which are measured with the help of sensors, wherein actual values of the print control marks determined in the process are compared with set point values for the print control marks in order to determine adjusting signals for the print-related process to be controlled based on a deviation between the actual values and the set point values. Such print control marks are typically printed on the substrate outside the actual print image or subject. Since such print control marks are perceived objectionable, smaller print control marks are increasingly employed which can have a diameter between 0.2 mm and 0.3 mm. These small print control marks, in addition to the round shape, can also have a rectangular, square or any polygonal or another shape, wherein these as a rule have an area of approximately 0.03 mm2 to approximately 0.07 mm2. Such small print control marks are also called micromarks. In particular when such small print control marks for controlling a print-related process are used, there is the problem that the actual values which are detected on such small print control marks can be affected by a major measurement inaccuracy or a major measurement error because of heavy stray light influences. For this reason, detecting utilizable actual values on such small print control marks, which can be utilized for a stable control of a print-related process, poses difficulties. Starting out from this, the present invention is based on the object of creating a new type of method for printing on a substrate.
According to the invention, at least one relatively small print control mark is printed in at least one printing zone of the substrate. In at least one printing zone of the substrate, at least one relatively large print control mark is additionally printed. The or each relatively small print control mark and the or each relatively large print control mark are detected with the help of a sensor. With the help of the measurement value of the or each relatively large print control mark, the actual values of print parameters detected through measurement of the relatively small print control marks are corrected. With the present invention it is provided, in addition to the at least one relatively small print control mark printed on the substrate, to print at least one relatively large print control mark on the substrate in order to correct the actual values of the print parameters detected on the relatively small print control marks based on a measurement value detected on the or each relatively large print control mark. A correction of actual values of the print parameters obtained on relative small print control marks is thus dynamically possible in the printing process, so that actual values obtained on such relatively small print control marks are also stable and reliable and can thus be utilized for controlling a print-related process with high control quality.
According to an advantageous further development of the invention, a relatively small print control mark is printed in at least one printing zone, namely in at least one color zone, of the substrate for all printed printing colors each, wherein for at least one printed printing color in at least one of the color zones a relatively large print control mark is printed, wherein the relatively small print control mark printed in the same color zone for the same print color and relatively large print control marks are detected with the help of the same sensor, and wherein based on the deviation between the measurement values of the relatively small print control mark and relatively large print control mark printed in the same color zone for the same print color the actual values of the print parameters detected in all color zones through measurement of the relatively small print control marks are corrected.
Preferentially, a relatively large print control mark is printed for each printed printing color in at least one of the color zones in each case, wherein the relatively small print control mark and relatively large print control mark printed in the same color zone for the same printing color are detected with the help of the same sensor, and wherein based on the deviation between the measurement values of the relatively small print control mark and relatively large print control mark printed in the same color zone for the same printing color, the actual values detected in all color zones for the same printing color through measurement of the relatively small print control marks are corrected. In particular when for each printing color a relatively large print control mark is printed on the substrate in addition to the relatively small print control marks, a particularly advantageous color density control and color register control is possible.
Preferentially, the relatively large print control mark of a printing color is printed onto the substrate in the immediate vicinity of a relatively small print control mark for the same printing color. In this way this ensures that the measurement values detected on the relatively large print control mark and on the relatively small print control mark are detected under identical measurement conditions, so that an advantageous correction of the actual values of the print parameters detected on the relatively small print control marks can then take place.
Preferred further developments of the invention are obtained from the subclaims and the following description. An exemplary embodiment of the invention is explained in more detail with the help of the drawing without being restricted to this.